In the case of a piezoelectric transformer, in a manner governed by its functional principle, a plasma is generated by means of a sinusoidal output voltage. In this case, the rising edges and the falling edges of the output voltage generated at the piezoelectric transformer have the same steepness. The generation of positive and negative ions in a process gas is largely dependent on the steepness of said edges. On account of the functional principle of the piezoelectric transformers, the steepness of the edges cannot be configured differently.
Consequently, the ratio of positive to negative ions in the plasma generated by the piezoelectric transformer is defined for a predetermined composition of a process gas.
However, there are numerous applications of atmospheric, non-thermal plasma in which the capability of setting a specific ratio of positive to negative ions is advantageous. These include, for example, applications in which atmospheric, non-thermal plasma is used for purifying water.